In recent years the function of the motor vehicle has been materially improved by electronic control systems. Through the use of digital electronics in the engine, it has been possible, for example, to reduce the consumption of fuel and the emission of toxic substances. Anti-skid control systems help to reduce braking distances while at the same time maintaining the steerability of the vehicle.
In the future, further functional improvements can be achieved for the motor vehicle, particularly by intermeshing the individual control functions instead of having each function operate separately. With an electronically controlled automatic transmission, gears can be shifted, for example, with less attendant wear of the clutch linings and more smoothly if the instant the gear is changed the engine torque is temporarily reduced by a suitable intervention into the electronic engine control system.
To meet these needs, it is necessary for the computer controlling the transmission to transmit relevant data to the computer controlling the engine at precisely the right instant. Until now, this has been accomplished by means of a series of single signal lines.
In more complex systems, however, the number of such signal lines becomes too large. In this case, therefore, a fast data transmission is necessary between the computers installed in the motor vehicle which requires few connections in the controller plug and provides for the transmission of data in coded form.
For this purpose, local area networks for coupling microprocessors, minicomputers and peripheral devices have been devised in the past, particularly for communications applications. Thus, there are a large number of state-of-the-art transmission protocols for the coupling of microcomputers including, for example, DDB (1), IIC (2), MUART (3), CSMA (4), SDLC (4) and HDLC (4). In this connection, reference may be made to the following:
(1) VALVO, DDB Specification;
(2) VALVO, Technische Informationen fu/ r die Industrie 811215;
(3) INTEL, Microprocessor and Peripheral Handbook, 1983; and,
(4) A. Tannenbaum, Computer Networks, Prentice Hall International, 1981.